A showdown vote, expected late in the day, marked the first chance for lawmakers to take a stand on the secret surveillance program since former NSA systems analyst Edward Snowden leaked classified documents last month that spelled out the monumental scope of the government's activities.

The issue created unusual political coalitions in Washington, with the Obama administration, national security leaders in Congress and the Republican establishment facing off against libertarian-leaning conservatives and some liberal Democrats.

With a flurry of letters, statements and tweets, both sides lobbied furiously in the hours prior to the vote in the Republican-controlled House. The director of national intelligence, James Clapper, warned against dismantling a critical intelligence tool.

Republican Rep. Justin Amash, chief sponsor of the effort, said it was designed to end the indiscriminate collection of Americans' phone records. His measure, offered as an addition to a USD 598.3 billion defense spending bill for 2014, would cancel the statutory authority for the NSA program, ending the agency's ability to collect phone records and metadata under the USA Patriot Act unless it identified an individual under investigation.

Amash stepped up the pressure on rank-and-file colleagues, looking ahead to meetings with constituents during next month's congressional break. "As you go home for August recess, you will be asked: Did you oppose the suspicionless collection of every American's phone records? When you had the chance to stand up for Americans' privacy, did you?" the Michigan Republican asked in a statement pleading for support for his measure.

Whatever the outcome in the House, the measure faces strong opposition in the Senate and from the White House and is unlikely to survive in a final spending bill. Since the September 11, 2001, attacks, Congress has authorized, and a Republican and a Democratic president have signed, an extension of the powers to search records and conduct roving wiretaps in pursuit of terrorists.

Two years ago, in a strong bipartisan statement, the Senate voted 72-23 to renew the Patriot Act and the House backed the extension 250-153.